The present invention relates generally to wireless communications and, more particularly, to a method for simulcast transmissions.
In recent years, there has been increased interest in building localized, private wireless telephone systems used by corporations or other organizations. Private wireless telephone systems employ many concepts and features used by conventional cellular networks and may be thought of as a scaled-down cellular network. A plurality of radio heads are positioned throughout the building or facility to provide radio coverage within the facility. The radio heads are connected to a central controller which, in turn, connects the private wireless telephone system with other networks, such as a public land mobile network or the public-switched telephone network.
One advantage of a private wireless telephone system is that it allows customers to use mobile terminals in an office or other localized area rather than a desk phone with a fixed connection to the telephone system. Thus, customers have freedom to move about within the facility, yet remain accessible by phone. The private wireless telephone system can also interface with the public land mobile network, allowing users of the private wireless telephone system to use the same mobile terminal in both networks. Thus, the user can move seamlessly between the private wireless telephone system and public land mobile network.
Many commercial deployments of private wireless telephone systems use a technique known as simulcasting on the downlink frequencies carrying the control channel. That is, multiple radio heads simultaneously transmit the same data from two or more base stations whose coverage areas may overlap. Simulcasting simplifies cell planning in the private wireless telephone system.
The present invention relates to a simulcasting method that is useful in wireless communication networks, such as a private wireless telephone system. Simulcast signals are transmitted from two radio heads whose coverage area overlaps. The simulcast signals comprise a plurality of frames, each frame comprising a plurality of bits. One or more bits in at least one of the simulcast signals is randomized in order to change the phase relationship of the simulcast signals from one frame to the next. By varying the phase relationship of the simulcast signals from one frame to the next, long nulls where the overlapping signals are 180xc2x0 out-of-phase are avoided.